Cranial Nerves Basics
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| Function of CN 1? | smells
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| Function of CN 2? | sees
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| Function of CN 3,4,6? | moves eyes, constricts pupils, accommodates
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| Function of CN 5? | chews and feels front of head
afferent loop of corneal blink
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| Function of CN 7? | moves the face, tastes, salivates, cries
efferent loop of corneal blink
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| Function of CN 8? | hears, regulates balance
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| Function of CN 9? | tastes, swallows, monitors carotid body and sinus
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| Function of CN 10? | tastes, swallows, lifts palate, talks, communication to and from thoraco-abdominal viscera
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| Function of CN 11? | turns head
lifts shoulders
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| Function of CN 12? | moves tongue
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| What 3 cranial nerves are purely sensory? | CN 1 olfactory
CN 2 Optic
CN 8 Vestibulocochlear
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| What 5 cranial nerves are purely motor? | 3 oculomotor
4 trochlear
6 abducens
11 accessory
12 hypoglossal
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| What 4 cranial nerves are mixed containing motor and sensory components? | 5 trigeminal
7 facial
9 glossopharyngeal
10 vagus
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| Which of the 5 mixed motor cranial nerves has a visceral component? | CN 3
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| Which of the 4 mixed cranial nerves has only 2 components, and what are the nuclei? | CN 5 trigeminal - somatic motor (motor nuc.5), somatic sensory (sens. nuc.5)
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| Which of the 4 mixed Cranial nerves have their visceral sensory components through the nucleus solitarius? | 7, 9, 10
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| What is the somatic motor nucleus of CN 7? | facial nuc.
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| What is the somatic motor nucleus of CN 9 & 10? | Nuc. aMbiguus
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| What are the visceral motor nuclei of 7, 9, 10? | 7 Sup. saliv. nuc.
9 Inf. saliv. nuc
10 dorsal mot. nuc.
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| In what portion of the brainstem does the sensory nucleus of 5 reside? | extends from the midbrain to the spinal cord
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| In what portion of the brainstem does the sensory nucleus of 8 reside? | Caudal pons and medulla
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| General rule for how CNs exit the brainstem? | they exit relatively anterior to the ventricular system and do not cross over to the opposite side on exiting from the brainstem
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| What CN is the exception to the same side no crossover rule? | CN 4, crosses over and passes over the roof of the brainstem
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| All autonomic CN fibers are of what functional type? | parasympathetic
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| What 2 CNs are involved in opening and closing the eye? | CN 7 closes eyes (like a hook pulling a window shade down)
CN 3 opens eyes (like 3 pillars)
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| Clinical difference between upper and lower motor neuron lesion of CN 7? | In LMN - the ipsilateral upper and lower face are paralyzed (eye won't close, forehead flat, nasolabial fold flattened)
In UMN lesion (stroke) - only contra. face below eyes paralyzed because of bilat. innervation of upper face by both hemispheres
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| The usual site of injury in Bell's palsy? | facial canal (which lies between the internal acoustic meatus and the stylomastoid foramen)
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| What auditory symptom can be expected in Bell's palsy? | hyperacusis, b/c the stapedius muscle is paralyzed and can't dampen the sound waves through the tympanic membrane
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| What is the clinical finding in an Intranuclear ophthalmoplegia (INO)? | A lesion of the MLF causes nystagmus of the abducting eye with absent adduction of the other eye.
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| How is the side of the INO lesion determined? | The lesion is on the side of the eye that should be adducting.
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| What is a clinical finding in bilateral INO? | this will be suspected if neither eye adducts with horizontal gaze.
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| Finding in unilateral lesion of left CN 12? | deviation to the lesion side (left) on tongue protrusion
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| Finding in bilateral lesion of CN 12? | slow and incomplete tongue movements, especially when moving side to side
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| The left cerebral hemisphere controls which SCM muscle and what function? | ipsilateral SCM muscle (left in this case) causes contralateral rotation ( right rotation in this example)
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| Why is it that a 6th nerve palsy may be a "false localizing sign"? | The reason for this is that it has the longest intracranial route of the cranial nerves, therefore it is the most susceptible to pressure that can occur with any cause of increased intracranial pressure.
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| Which functions should be tested when evaluating CN 9 & CN 10? | voluntary - aah/swallow
involuntary - gag reflex, has sensory and motor limb
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| How to distinguish bulbar (LMN) from pseudobulbar (UMN) palsy? | unilateral LMN lesion - paresis of palate on lesioned side, uvula deviates to high/normal side
bilateral LMN lesion - absent voluntary and reflex activity
UMN lesion - must have bilateral palatal weakness (nuc. ambiguus), with hyperactive gag reflex
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| What are the sensory functions of CN 9 & CN 10? | sensation for the pharynx and taste for the posterior one-third of the tongue.
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| What cranial nerves nuclei are located in the medulla and have localizing value for lesions in this most caudal part of the brainstem? | Cranial nerves 9,10,11, and 12
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| How to check cochlear division of CN 8? | check auditory acuity and rinne/weber test
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| Neurologically caused unilateral hearing loss is almost always caused by damage to what structures? | lesion/damage in cochlea sensory organ, the spiral ganglion, the cochlear nerve, or cochlear nucleus
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| How do you clinically test the vestibular portion of CN 8? | test balance, and with the oculocephalic reflex (Doll's eye maneuver) and oculovestibular reflex (ice water calorics).
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| Describe pathway of the axons for the descending tract of the 5th cranial nerve (pain and temperature)? | axons descend to the level of the upper cervical spinal cord before they synapse with neurons of the nucleus of the descending tract of the 5th nerve. Second order neurons then cross over and ascend to the VPM nucleus of the thalamus.
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| Eye movements are controlled by 4 major oculomotor gaze systems, list them? | Saccadic (frontal gaze center to PPRF
Smooth Pursuit (parietal-occipital gaze center via cerebellar and vestibular pathways)
Vestibulo-ocular (vestibular input)
Vergence (optic pathways to oculomotor nuclei) to keep image on fovea
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| Function of the MLF? | The medial longitudinal fasciculus connects the 6th nerve nucleus in pons to the contralateral 3rd nerve nucleus in midbrain for conjugated eye movements.
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| What subjective sign results when CN 3, 4 and 6 don't work in concert for conjugate eye movements? | diplopia (double vision) results.
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| The 4th CN supplies which muscle and therefore what ocular movements? | the superior oblique muscle, which is important to looking down and in (towards the midline).
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| Which is the only sensory modality with direct access to cerebral cortex without going through the thalamus? | Olfaction. The olfactory tracts project mainly to the uncus of the temporal lobes.
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